1. Field of the Invention
The present invention relates to a method for manufacturing steel parts for an automotive automatic transmission in which a desired portion of steel part for an automotive automatic transmission using an alloy steel for machine structural use as a material is copper-brazed at a high temperature and then this part is quench hardened.
2. Description of the Related Art
A joint portion of steel parts for an automotive automatic transmission is copper-brazed at a high temperature so that the parts can sufficiently withstand a load applied to the parts at the time of their operation. Also, the parts must be quench hardened because they are functional parts.
The high-temperature copper brazing and subsequent quench hardening treatments of the parts have been carried out by various methods.
For example, Japanese Patent Publication No. 63-54929 and Japanese Patent Laid-Open No. 4-327031 have disclosed methods in which parts are heated in batches to be subjected to high-temperature copper brazing and quench hardening. With these methods, because the parts are treated in batches, troublesome work is required, and also there remain questions as to whether oxidation or removal of chromium contained in the alloy steel for machine structural use forming the parts can be prevented and whether removal of carbon from the steel can be prevented.
The alloy steel for machine structural use, which has been exposed to a high temperature to be copper-brazed, is rapidly cooled to a temperature of approximately 550° C. below the Ar1 point generally common to the steels of this kind, and then allowed to cool by means of air cooling etc. to prevent a deposit from being produced in the steel and the structure from being made rough. The steel parts for an automotive automatic transmission are reheated to a temperature of 830 to 880° C. above the Ac3 point after they are rapidly cooled and air cooled after copper-brazed in this manner, by which the structure is austenitized and quench hardened.